This invention relates to telephone systems and more particularly to telephone circuits employing key telephone systems.
Existing key telephone systems having the capabilities for outside as well as internal communications require the use of two subsets or placing the outside call on hold while the internal call is conducted. In either case, this requires depressing many buttons or manipulating several subsets to perform the desired operation.
There are several shortcomings to the above operating procedures. If the two subset approach is used, there is always the inconvenience of holding the two subsets. If the single subset is used in conjunction with the hold button, the outside party who is calling for some type of assistance does not have the assurance that anything is being done to solve his problems since he does not hear any part of the conversation that transpires internally.
A solution to this problem is disclosed in my copending application Ser. No. 622,287, filed Oct. 10, 1975. A circuit arrangement is disclosed in this copending application that will enable one party to have a two-way conversation simultaneously with an outside party and an internal party without the outside party and inside party hearing each other. A button is provided to actuate circuitry in the circuit arrangement to place all three parties in a two-way conference.
One disadvantage with the circuit arrangement of this copending application is that the sidetones in the receiver of the subset of the one party is undesirably high.